Published: May 28, 2003
Updated: Nov. 3, 2004
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By Duke Medicine News and Communications
SAN FRANCISCO -- In findings that should add to the national debate over rising obesity rates in the U.S., Duke University Medical Center researchers have demonstrated that physical inactivity leads to a significant increase in potentially dangerous visceral fat, while high amounts of exercise can lead to significant decreases in such fat over a fairly short time period.
The researchers also found that while lower amounts of exercise prevented the significant accumulation of visceral fat seen in the controls, it did not lead to the improvements seen in participants with higher levels of exercise.
Controlling visceral fat is important, the researchers say, because increased levels have been associated with insulin resistance, cardiovascular disease and other metabolic syndromes. Visceral fat is located around the organs inside the belly and is deeper in the body than subcutaneous fat, which lies under the skin.
In the first randomized clinical trial to evaluate the effects of varying amounts and intensities of exercise in sedentary overweight men and women, the researchers were surprised at how rapidly fat accumulated deep in the abdomens of study participants who did not exercise. This rapid accumulation of visceral fat emphasizes the high cost of a sedentary lifestyle.
"The results of our investigation show that in sedentary overweight adults who continue to choose a sedentary lifestyle the detrimental effects are worse and more rapid than we previously thought," said Cris Slentz, Ph.D., who presented the results of the Duke study today (May 28, 2003) during the 50th annual scientific sessions of the American College of Sports Medicine. "We probably should not have been surprised since this simply mirrors the increasingly rapid rise in obesity prevalence seen in the U.S., where presently two out of three adults are overweight or obese.
"On the other hand, participants who exercised at a level equivalent to 17 miles of jogging each week saw significant declines in visceral fat, subcutaneous abdominal fat and total abdominal fat," Slentz continued. "While this may seem like a lot of exercise our previously sedentary and overweight subjects were quite capable of doing this amount."
Specifically, participants who did not exercise had an 8.6 percent increase in visceral fat after eight months, while those participants who exercised at the highest amount saw a 8.1 percent decrease in visceral fat.
Additionally, the Duke team found interesting difference between men and women.
"In the group of subjects who did not exercise, the men had a 1.5 percent increase in weight, while the women had a 0.6 percent increase," Slentz said. "However, the women experienced an 11.6 percent increase in visceral fat, more than twice the amount of the men (5.7 percent). That the women experience less of a weight gain but gained a higher proportion of visceral fat suggests an aggressive accumulation in women that needs further study."
To better understand the effects of differing amounts of exercise, the researchers randomized 170 participants into one of four groups: no exercise, low dose/moderate intensity (equivalent of 11 miles of walking per week), low dose/vigorous intensity (11 miles of jogging per week) or high dose/vigorous intensity (17 miles of jogging per week).
The exercise was carried out on treadmills, elliptical trainers or cycle ergometers in a supervised setting. In order to determine the role of exercise alone, participants were not allowed to change their diet during the course of the study. The researchers used computed tomography (CT) both before exercise and eight months later to determine the extent and distribution of fat change.
"There were no significant changes in visceral, subcutaneous or total fat in either of the low exercise groups for men or women, which suggest that this amount of exercise is adequate to prevent significant gain in fat around the stomach and that the amount of exercise is more important than the intensity," Slentz said. "The data emphasizes the high cost of continued physical inactivity, the preventative abilities of modest amounts of exercise, and the substantial benefits to be gained by performing 50 percent more exercise each week (17 versus 11 miles per week)."
The Duke team was led by cardiologist William Kraus, M.D., who received a $4.3 million grant from the National Heart, Lung and Blood Institute in 1998 to investigate the effects of exercise on sedentary overweight adults at risk for developing heart disease and/or diabetes. The results of that five-year trial, dubbed STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise), are now being published and presented.
Joining Slentz were Duke colleagues, Lori Aiken, Brian Duscha, Johanna Johnson, Kevin Ketchum, Leslie Kelly, and Kraus. Joseph Houmard, Ph.D., and Chuck Tanner from East Carolina University, were also members of the team.